(Adapted from applicant's abstract): Project 4 proposes to examine whether exposure of the human fetal CNS to HIV-1 may cause alterations in normal myelination. These changes may be a part of the basis for the neurologic dysfunction characteristic of pediatric AIDS. A 3-part research protocol has been designed to test this hypothesis: the first component will examine myelination qualitatively and quantitatively in fetal CNS tissue exposed to HIV-1 in utero; the second part of this study will use an in vitro organotypic explant model of human fetal CNS cells and focus on oligodendrocyte differentiation.